1. Field of the Invention
The present invention relates to a lightweight helmet shell and a method for manufacturing the same. More particularly, the present invention relates to a lightweight helmet shell including an outer shell formed from a breathable compressed fiber sheet shell, which has excellent breathability, is lightweight, and has improved impact absorbability, and a method for manufacturing the same.
2. Description of the Related Art
Helmets worn to prevent injuries during outdoor leisure activities such as motorcycling, motor racing, inline skating and horse riding, are essentially required to absorb impact efficiently as well as to undergo minimal damage due to the impact, when the helmets happen to collide with the ground or any other objects.
In general, a helmet has, in its outer part, a helmet shell that is constituted of a helmet outer shell, which is produced to maintain the basic shape of the helmet and to have appropriate impact absorbability so as to absorb any impact exerted to the helmet and to prevent the impact from being transferred to the helmet wearer, and a helmet inner shell which lies beneath the outer shell and mitigates the impact exerted to the outer shell. The inner part of the helmet, which is also the inner part of the helmet shell, is lined with a liner or the like that gives a good feeling of wear when the wearer's head is in contact with the helmet.
Among these, in order to satisfy the requirements as described above, the helmet shell is required to have appropriate impact absorbability to the extent of being capable of maintaining the original external shape without undergoing deformation under impact. On the other hand, the helmet shell also needs to have toughness, since there is a risk of breakage at the time of collision if the rigidity of the helmet shell is excessively high. In addition to these, the helmet shell also needs to satisfy the requirement of having a small specific gravity, in order to make the feeling of wear pleasant.
Most of the helmet shells produced so far have been produced with fiber-reinforced plastics so as to satisfy the requirements as described above. Fiber-reinforced plastics are products obtained by incorporating fibers such as glass fiber, carbon fiber and aramid fiber, into thermosetting resins such as unsaturated polyesters and epoxy resins. These materials can be easily processed and can be produced into relatively thin sheets while still maintaining high strength and impact absorbability. Thus, fiber-reinforced plastics are materials that satisfy the above-described requirements to a certain extent.
However, since the fiber-reinforced plastics basically make use of thermosetting resins, as a matter of fact, they have insufficient toughness as compared with thermoplastic resins, and because of the insufficient toughness, helmet shells often undergo breakage when a large impact is exerted thereon. Prevention of such breakage needs to increase the thickness of the helmet shell, which leads to an increase in the production cost, as well as a problem of worsening the feeling of wear due to an increase in the weight of the helmet. In an attempt to solve such problems, the helmet outer shell was once produced using a thermoplastic resin. These fiber-reinforced plastics are constituted such that a resin matrix is provided as a base, and various organic and inorganic fibers, non-woven fabrics, knitted fabrics and the like are completely embedded in the resin matrix for the purpose of complementing the properties of resin. According to the recent trends in technology, such a resin matrix is used as a base and is formed to have a minimal thickness, and a lightweight material such as a fiber, a knitted fabric or an expanded material is formed on any one side or on both sides of the resin matrix.
According to Korean Patent Application No. 10-2004-0004746, it is reported that the weight of a conventional multilayer-structured helmet shell is reduced by 40% by replacing the outermost layer of the helmet shell with an ultrahigh molecular weight porous polyethylene. However, since a fiber-reinforced plastic layer should be essentially included in the multilayer structure, the overall rate of decrease in the weight of the multilayer structure is only less than 20%, and thus the helmet shell as a whole does not undergo sufficient weight reduction.
Korean Patent Application No. 10-2003-0054927 proposes a helmet shell formed from a hybrid complex material, which is formed by laminating a fiber-reinforced plastic layer and a highly elastic fiber-reinforced thin film complex material on the outer surface of a helmet inner shell produced by molding an expanded plastic material. However, this helmet shell also includes a fiber-reinforced plastic layer, and thus still has a problem of the weight reduction being insufficient.
Korean Patent Application No. 10-1993-0017354, Korean Patent Application No. 10-2000-0018132, U.S. Pat. No. 3,958,276, Japanese Patent Application No. 7-72907, Japanese Patent Application No. 7-189447, and Japanese Patent Application No. 2002-351348 suggest using a fiber network structure or a flexible fiber structure. However, these fiber structures are also involved in the formation of fiber-reinforced plastic (FRP) layers, and therefore, the technical limitation in the related art as described above has not yet been overcome.
U.S. Pat. No. 7,062,795 suggests using layers reinforced with a high strength network structure provided on the inner side and the outer side of a fiber-reinforced plastic layer, and there is still a problem that weight reduction is not achieved sufficiently.
As such, the technologies of the related art essentially involve the introduction of a fiber-reinforced plastic layer as a factor basically constituting the outermost layer of a helmet shell, and adopt the form in which such a fiber-reinforced plastic layer, and a material selected from porous or highly elastic materials having relatively low specific gravities, fibers, woven fabrics, knitted fabrics, non-woven fabrics, expanded materials, fiber-reinforced thin film materials and the like, are introduced and laminated in combination.
A helmet shell produced by a method such as described above has its weight reduced to a certain extent, but still has a problem that the weight reduction is not sufficient.